Big powers leave Iran nuclear talks empty-handed

World powers failed to prise any change from Iran in two days of talks on its nuclear programme, with the EU and United States calling the discussions disappointing and saying no further meetings were planned.

"This is not the conclusion I'd hoped for," European Union foreign policy chief Catherine Ashton said at the end of the talks in Istanbul. "I am disappointed."

That was echoed by a senior US official, but he said talks had not broken down and been "very businesslike, but difficult."

The best that the six world powers -- the United States, France, Germany, China, Russia and Britain -- can hope for is that Iran rethinks its position, once chief negotiator Saeed Jalili reports back to Tehran.

"We now wait to hear... whether Iran will respond on reflection," said Ashton, the lead negotiator for the six world powers.

An aide to Jalili told reporters that there would be another round of talks, even if the timing and venue were undecided. But Ashton said further talks depended on a more constructive approach from Tehran.

"The process can go forward if Iran chooses to respond positively," she said. "The door remains open. The choice remains in Iran's hands."

The powers have offered a nuclear fuel swap that would effectively reduce Iran's reserves of low enriched uranium to levels too small to be used to make a bomb. But Iran would have to drop pre-conditions for a deal to happen.

"We proposed the possibility of an experts-level discussion of the details... The Iranians at this stage are not prepared to do that, we came back to the issue of preconditions," the US official said.

The West suspects Iran wants to develop nuclear weapons while Tehran says its atomic energy program is peaceful.

The standoff has dragged on for eight years and expectations were low heading into the Istanbul talks.